We have come across the permanent "yes" answer in many countries. Our first experience was in India. We had gone for a long walk along the beach and it was starting to get dark so we decided to catch the bus back.
Arriving at the bus stop we asked the first person who came past if it was the right place to catch the bus to Baga and were told yes.
The next person we asked did the Baga bus stop here and they told us yes.
Next question was is the Baga bus coming soon and yes you can guess - the answer is yes.
I think we went through a few more questions until I gave it some thought and asked the next person, "what time is the next bus to Baga?" and he said "tomorrow morning".
Needless to say we did not wait but hitched a ride!
Many people do not like to offend by giving a negative answer so it is better to ask a question that cannot be answered by yes or no - however even today it sometimes takes us a few yes's before we remember this.